Color filters are used for liquid crystal displays (LCD), optical filters for cameras, and the like. Color filters may be fabricated by coating a fine region with three or more colors on a charge-coupled device or a transparent substrate. Methods for making a colored thin film include dyeing, printing, electrophoretic deposition (EPD), pigment dispersion, inkjet printing, and the like. Currently, such methods are used in the manufacture of LCDs for mobile phones, laptops, monitors, TVs, and the like.
The dyeing method forms a colored film by forming an image on a glass substrate with a dyeing agent and then dyeing the image with direct dyes. Examples of dyeing agents used in fabricating colored thin films include natural photosensitive resins such as gelatin, amine-modified polyvinyl alcohols, amine-modified acrylic-based resins, and the like. However, the dyeing process may be complex and lengthy, since it should include resist-printing whenever a color needs to be changed to form a multicolored thin film on the same substrate. In addition, many generally-used dyes and resins may have good color vividness and dispersion but also poor color fastness, water resistance, and heat resistance, which are very important characteristics.
The printing method forms a colored thin film by printing an ink prepared by dispersing a pigment into a thermally curable or photocurable resin and curing it with heat or light. This method may decrease material costs compared with other methods, but it is difficult to form a fine and precise image and to acquire a uniform thin film layer. Korean Patent Laid-Open Publication No. 1996-0011513 discloses formation of a color filter in an inkjet method. However, the resultant color filter suffers similar problems to a color filter made in the dyeing method, for example, deteriorated durability and heat resistance, because a dye-type color resist composition that is dispersed from a nozzle is also used to accomplish fine and precise color printing.
Korean Patent Laid-Open Publication No. 1996-0029904 discloses formation of a color Merin an electrophoretic deposition (EPD) method using an electrical precipitation method. The electrophoretic deposition (EPD) method may accomplish a precisely-colored thin film having excellent heat resistance and color fastness, since it uses a pigment. However, this method may not be applicable for a very precise color filter requiring a finer electrode pattern for a more precise pixel in the future, because a colored thin film may be stained or thicker at both ends due to electrical resistance.
The pigment dispersion method forms a colored film by repeating a series of processes such as coating, patternwise-exposing to light, removing non-exposed part using a solvent, and heat-curing a photopolymer composition including a coloring agent on a transparent substrate including a black matrix. This method can improve heat resistance and durability, which are very important characteristics for a color filter, and can provide a uniformly-thick film.
In this pigment dispersion method, a photosensitive resin composition for a color filter generally includes a binder resin, a photopolymerization monomer, a photopolymerization initiator, a pigment, a solvent, and other additives.